1. Field of the Invention
The present invention relates to electronically controlled mechanical timepieces that accurately drive pointers fixed to a wheel train bridge  by using a generator to convert mechanical energy in the unwinding mode of a spring into electrical energy, and controlling the rotation cycle of the generator by driving a rotation control circuit with the electrical energy, and to control methods therefor.
2. Description of the Related Art
An electronically controlled mechanical timepiece described in Japanese Examined Patent Publication No. 7-119812 is known as one for indicating an accurate time that accurately drives pointers fixed to a wheel train bridge  by using a generator to convert mechanical energy in the unwinding mode of a spring into electrical energy, and controlling a current flowing in the coil of the generator by driving a rotation control circuit with the electrical energy.
In the electronically controlled mechanical timepiece, by inputting a signal based on the rotation of the generator into a counter while inputting a signal from a quartz oscillator into the counter, comparing values in the counter, and controlling the generator based on the difference, rotation velocity is controlled. The counter compares the phase differences of reference clock pulses (Ref-pulses) and generator-rotation-cycle pulses (G-pulses), and increases the value of a U/D counter if the G-pulses are ahead, or decreases the value if the G-pulses are behind. The counter consists of a so-called integral counter.
When a value obtained by measuring the time of one cycle of the Ref-pulses is equal to a value obtained by the integral counter, braking of the generator is performed, and braking is continuously performed until measurement of the time of one cycle of the Ref-pulses terminates. Accordingly, the value of the integral counter sets a braking release time. That is, the value of the integral counter is multiplied by braking release time N at which the average velocity of the G-pulses is equal to a target velocity (Ref-pulses). In other words, integral control is employed in this system.
According to the integral control, the average velocity of a rotor over a sufficient duration can be controlled to a velocity in a set time, whereby pointers can be accurately moved at a controlled velocity because signals output in each cycle are compared, while the signals are being counted. However, the integral control has a problem in that the rotation velocity of the rotor cannot be instantly adjusted, which causes slow responsiveness. The integral control also has a problem in that a plurality of phase excursions is generated until the relationship between spring force and braking force is set so as to correspond to a target frequency.
The integral control can be expressed in the block diagram in FIG. 20.
In general, it is known that a transfer function used for a generator or motor is 1/s(sT+1). This consists of a first-order-lag transfer function 101 and an integral term 102 of 1/s. Accordingly, an integral factor is included in the generator as an object to be controlled. Bode diagrams on the assumption that only the integral control is performed for the object are shown in FIGS. 21 and 22.
In the Bode diagrams, it is required as a condition for stable rotation control that a phase allowance, i.e., the phase at a gain of zero db (gain intersection), be ahead of xe2x88x92180xc2x0 and that gain allowance, i.e., the gain at a phase of xe2x88x92180xc2x0 (phase intersection), be not more than zero db.
However, in the case where only the integral control is performed, a phase delay of xe2x88x9290xc2x0 occurs in the object, and a further phase delay of xe2x88x9290xc2x0 occurs due to the integral control, as shown in FIG. 21, so that the phase is at approximately xe2x88x92180xc2x0. Thus, stable control is difficult because the integral control alone cannot obtain phase allowance and gain allowance. Accordingly, the timepiece in Japanese Examined Patent Publication No. 7-119812 must perform control at a very low frequency, and its responsive characteristic is positioned at approximately 0.016 Hz or less.
A case where the gain of the integral counter is set to be 100 times greater is shown in FIG. 22. Also, in this case, phase allowance is behind xe2x88x92180xc2x0, and stable control cannot be anticipated.
As is clear from the above-described data, by performing control using only the conventional integral control, average velocity control can be performed, but a problem occurs in that phase excursions cannot be eliminated.
In addition, slow control response causes a problem in that almost nothing can compensate for a rapid disturbance as in the case when acceleration is generated in a watch by a swing of an arm.
It is an object of the present invention to provide an electronically controlled mechanical timepiece that is free from phase excursions and has rapid control system response, and to a control method therefor.
According to the present invention, there is provided an electronically controlled mechanical timepiece including: a mechanical energy source; a generator driven by the mechanical energy source connected to the generator via a wheel train bridge , which generates induced electric power for supplying electric energy; a brake circuit for braking the generator; pointers joined to the wheel train bridge ; and a rotation control circuit for controlling the rotation cycle of the generator by controlling the brake circuit; wherein the rotation control circuit includes: a rotation detection circuit for generating a rotation signal of the generator; a target-signal generating circuit for generating a target signal corresponding to a target number of revolutions; and a phase-difference compensating circuit for detecting the phase difference of the target signal output from the rotation detection circuit, and the target signal output from the target-signal generating circuit, and outputting a phase-difference compensation signal which is used as a braking control signal in the brake circuit.
An electronically controlled mechanical timepiece of the present invention uses a mechanical energy source such as a spring to drive pointers and a generator, and controls the number of rotations of a rotor, i.e., the pointers by braking the generator. At this time, the electronically controlled mechanical timepiece compares the phases of a rotation signal of the generator and a target signal such as a timepiece""s standard signal, and inputs based on the phase difference a brake control signal to a brake circuit for the generator, whereby a so-called phase-synchronization circuit or phase-locked-loop control (PLL control) is realized in an electronically controlled mechanical timepiece. Accordingly, since a braking level can be set by comparing the waveforms of generated power in each cycle, the activation of a locked range realizes a stable, rapidly responsive system and enables the elimination of phase excursions unless the waveforms of generated power remarkably change suddenly.
Under these circumstances, it is preferable that the generator and the brake circuit constitute a voltage-controlled oscillator, and that the phase-difference compensating circuit include: a phase-comparison circuit for comparing the phases of the rotation signal and the target signal; and a brake control circuit for inputting to the voltage-controlled oscillator the phase-difference compensation signal for controlling the brake circuit based on an output from the phase-comparison circuit.
Under these circumstances, it is preferable that the rotation control circuit include a waveform shaping circuit for converting the output waveform of the voltage-controlled oscillator into rectangular-wave pulses, and outputting as the rotation signal to the phase-comparison circuit.
The output waveform of the voltage-controlled oscillator changes in accordance with a control method therefor. However, by providing the waveform shaping circuit, the different part of the output waveform can be absorbed, and rectangular-wave pulses capable of being compared with a time standard signal can be output to the phase-comparison circuit, irrespective of the output waveform from the voltage-controlled oscillator. Thus, the phase-comparison circuit, etc., can be used in common to enable a reduction in a component cost.
In addition, it is preferable that the rotation control circuit include a frequency-to-velocity converter for converting the frequency of an output signal from the voltage-controlled oscillator into velocity, and that the brake control circuit be capable of outputting a signal which controls the brake circuit, based on an output from the phase-comparison circuit and an output from the frequency-to-velocity converter.
By providing the frequency-to-velocity converter, the time constant of a control circuit can be reduced, and responsiveness can be further improved.
Moreover, it is preferable that the phase-difference compensating circuit include a phase-difference detection circuit and a compensation-signal generating means for receiving an output from the phase-difference detection circuit that the rotation signal and the target signal be repetitive pulses, that the phase-difference detection circuit include counters for counting the numbers of rises or falls of the respective signals, and that one counter be incremented or decremented when the target signal rises or falls, or is incremented or decremented when the rotation signal rises or falls, and outputs an output of the counter as a phase-difference signal to the compensation-signal generating circuit.
By using a counter to constitute the phase-difference detection means, circuit arrangement can be simplified, and a cost can be also reduced. In addition, a counter capable of holding a plurality of counts can be used. Thus, a phase difference in a broad range can be detected, and even if phase differences are totaled, the total can be held. Accordingly, control in accordance with a total of phase differences can be performed, and more accurate velocity-controlled control can be performed.
Under these circumstances, it is preferable that the phase-difference detection circuit include: an integral counter for measuring a total of the phase excursion periods of the rotation signal and the target signal; a proportional counter for measuring phase excursion periods; and an adder for increasing or reducing the value of each counter in accordance with a lead or lag of the phase excursion of the rotation signal with respect to the target signal.
According to the present invention, there is provided a control method for an electronically controlled mechanical timepiece including a mechanical energy source; a generator driven by the mechanical energy source connected to the generator via a wheel train bridge , which generates induced electric power for supplying electric energy, a brake circuit for braking the generator, pointers joined to the wheel train bridge , and a rotation control circuit for controlling the rotation cycle of the generator by controlling the brake circuit, wherein a rotation signal of the generator and a target signal generated in accordance with a target number of revolutions are compared to detect the phase difference therebetween, and a phase-difference compensation signal in accordance with the phase difference is used to control the brake circuit.
In the present invention, phase excursions can be eliminated, and stable, rapidly responsive control system is realized because an electronically controlled mechanical timepiece can be controlled by phase-synchronization circuit control (PLL control).
Under these circumstances, it is preferable that the control method comprise: using an integral counter to measure a total of the phase excursion periods of the rotation signal and the target signal, and using a proportional counter to measure phase excursion periods; determining a lead or lag of the phase excursion of the rotation signal with respect to the target signal; computing a phase-difference compensation signal for setting a braking time by increasing or reducing the value of each counter in accordance with the determined result; and using the phase-difference compensation signal to control the brake circuit. The setting of the braking time includes not only the case where a braking time is directly set, but also the case where indirect braking is performed by setting a braking release time in which braking is not performed in a predetermined cycle.